The definition of a palpitation is an awareness or feeling of your heart beating. A PVC is a premature ventricular contraction and a PAC is a premature atrial contraction. Both are also known as extra systols, or in layman's terms an "early" or "extra" heart beat. Both are also likely to cause you to feel your heartbeat, thus a palpitation. This is not always the case though. You can have them without feeling them. Hope this sheds some light on your question.
"Now faith is the substance of things hoped for, the evidence of things unseen." ~ Hebrews 11:1 ~